By modified, I am referring more to carb (39mm Keihin), pipe/silencer (Paul Turner pipe and stock silencer) and airbox (see pic below) mods and not so much porting. I have spoken to a few people (both on the forum and locally) that after hearing about the issues i have experienced and shown here

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strongly recommended I do not run standard pump gas and stated that more than likely, this is at the root of my issues. Still working through the piston problems and wanted to get a feel for what everyone is using out there to either help confirm or eliminate this as the source of my problem. It has been going on too long.

Pic of air box lid - 3" intake and automotive cold air elbow. Silencer shown has been replaced with stock:



Thanks in advance.

i've had 3 pilots,current one is bored out to 500 and has 175-180 psi compression so I was running race gas in it half n half with 93 octane then switched over to just running A/v gas and its been fine.
My other 2 pilots had larger carbs and pipes and I used 93 octane with no problems but I've read on here some people swear by the a/v gas,it's certainly not going to hurt you to use it and if it gives you piece of mind then do it,but the only reason I use it is because my compression is so high.

Your squish band and compression rate is what is going to dictate whether or not you need to run race gas. Just the addition of a larger carb, pipe and porting do not require higher that 91 octane gas.

You will however need to raise the amount of fuel intake due to the increased air flow through the Engine.

Rand

I would if I was you. That way you have a guarantee from CO.
Good luck with new rebuild.